1. Field of the Invention
The purpose of the invention is to provide a wheelchair system that allows for independent positioning of the push rims and drive wheels, allowing for improved stability and improved shoulder biomechanics. The approach also allows for the addition of multispeed fixed-gear hubs for improved propulsion on sloped surfaces and allows for removal or backward rotation of the push rims for easier transfers in and out of the wheelchair.
2. Related Art
The most common form of a manual wheelchair 100 utilizes a push rim 110 connected directly to the drive wheels 120 as shown in FIG. 1. The wheelchair user is able to propel the wheelchair 100 by pushing the push rims 110 with their hands, thereby rotating the wheel an equal angle and translating the chair forward. The common wheelchair is elegant in its simplicity. However, the inherent mechanical coupling of the push rim 110 and the wheel 120 require that they be placed in the same fore-aft position, which may lead to reduced stability of the wheelchair and/or shoulder problems. In setup of the common wheelchair, the clinician must balance concerns of shoulder biomechanics and stability of the wheelchair. On one hand, the clinician would like to move the push rims forward to promote a better positioning of the shoulders for propulsion. On the other hand, the axle of the wheels 120 must remain behind the center of gravity 130 to reduce the likelihood the wheelchair 100 will tip over backward. A common approach is to move the push rim/wheel combination 110/120 as far forward as possible while still maintaining a stable base 150 of support of the wheelchair by positioning the drive wheel 120 and front casters 140 to frame the center of gravity 130 in fore/aft directions.
The positioning of the push-rim/wheel 110/120 combination in common wheelchairs leads to difficulties in transfers (transferring in and out of the wheelchair 100). For example, the user must position the wheelchair at an angle with a bed 200 or other transfer surface in order to use a transfer board 210 (see FIG. 2). Without a transfer board, the person must elevate their body a significant distance to clear the wheel of the wheelchair (FIGS. 3A, 3B).
Therefore, what is needed is a system and method that overcomes these significant problems found in the conventional systems as described above.